 Hi everyone, I am Dr. Ashwin Lavande. I am a practicing radiologist at Dr. Mukun Joshi's clinic since the last 17 years and practicing musculoskeletal ultrasound and guided interventions since the last 15-16 years. In today's workshop, we will be seeing how we scan peripheral nerves on ultrasound and we will be concentrating more on the upper limb nerves. So now we start examining the median nerve first. So any peripheral nerve if you see, it's a hypoechoic structure made up of multiple black dots giving a honeycomb appearance the short axis. So that's the median nerve in the mid forearm where you see the honeycomb like appearance medial to the brachial artery lying over the brachialis muscle. Further if you come down, it will go at the elbow level in between the two muscles. It's the pronator theories and the underneath that is the brachialis. So the nerve is going in between the pronator theories and the brachialis at the elbow level and further if you go down, it goes between the two heads of pronator. So this is the place, this is the pronator tunnel where it can get compressed and for this you need to do a pronation supination kind of a dynamic examination. So in this, you have to evaluate whether there is dynamic entrapment or dynamic compression of the nerve or impingement of the nerve at this level. In the short axis, these are the two heads of pronator. If you go proximally, you see the nerve between the pronator and the brachialis. If you come distally, that's the pronator tunnel where the two heads are there and then the nerve finally exits and comes into the flexor compartment in the fat plane between the FDS and the FDP group of muscles. And then you can trace the nerve all the way up to the med forearm. So now we trace the nerve further distally in the medial forearm. So here we are at the level of the pronator quadratus. You can see the fibers of the pronator quadratus in the axial plane. The medial nerve is lying between the FDS and FDP group of muscles. They are forming the tendons at this level and distally if you can see, the nerve is located medial to the FCR tendon and is located over the FDP group of tendons with the FDS lying medially and the FPL tendon lying lateral and a little deeper. So the thin hypoechoic line which you see, curvilinear line which you can see on top of it is the facial plane. And then if you go distally, you can see thickening of that same plane and this is the flexor retinaculum which you can appreciate now. That's the medial nerve underneath it and which is hypoechoic lying on the ecogenic flexor tendon. So the tendons are ecogenic as compared to the nerve and show a classical fibroler echopattern. On the radial aspect, that's the radial boundary of the proximal carpal tunnel. That's the scaphoid. The FCR tendon is located external to it. If you go medially, you will see the pesiform bone where the medial boundary of the flexor retinaculum is. The under artery and the nerve are located in the gyan's canal over it. Then if you go distally, the flexor retinaculum thickens. You can appreciate that and a little distal to that, you can see the distal boundaries of the flexor retinaculum. So laterally you will see the tubercle of trapezium and medially you will see the hook of hammit. That's the median nerve on the flexors and here it exits the carpal tunnel and then divides into the common digital nerves. So in the long axis, that's your median nerve exiting the carpal tunnel. This is in the distal carpal tunnel, proximal carpal tunnel and then this is the place where it goes into the distal fora. So when a patient comes with carpal tunnel syndrome, what we are supposed to measure and evaluate the median nerve. So what we do is we measure the cross sectional area of the median nerve in the distal forum at this level. Then we go further distally and measure the place where it's maximally enlarged somewhere in the proximal carpal tunnel or a little proximal to the flexor retinaculum there. A cross sectional area here then you go further down and see for its compression here in the distal carpal tunnel where it commonly gets compressed. You measure the flattening ratio, you measure the transverse diameter, you measure the AP diameter, divide the transverse by the AP and if the nerve is flattened then the flattening ratio should be more than 3.5 to 4 to call it a significant compression. And then you have to see for the nerve enlargement distally, distal to the flexor retinaculum at this level. So we have to see for enlargements proximal and distal to the tunnel, measure the cross sectional areas. So the difference is more than 4 as compared to the proximal if it is higher than 4, more than 4 millimeter square as compared to the distal forum cross sectional area then it is significant and warrants a surgical decompression. In the carpal tunnel we have to see the flexor tendons, we have to see whether there is synovitis surrounding the flexors as you can appreciate here. The patient will move her four fingers and you can see how the nerve dances on the flexors side to side. This movement should be there and the flexors should not be spaced by that hypoechoic synovial tissue. So here there is no synovial tissue, it is a normal case so you would see the flexor tendon there is no gap between the flexors otherwise if there is synovitis there will be gap between the flexors. Other than the most important thing which the surgeon needs to know before carpal tunnel release is a location of the parmacutinase branch of the median nerve. So if you can appreciate here that is the median nerve main trunk and if you see along the radial aspect closely there is a small tiny dot structure which is coming along the radial aspect if you can appreciate here that is the parmacutinase branch of the radial nerve which will cross the flexor retinaculum and go superficial to it. So the most important thing which surgeon needs before the carpal tunnel release is the location of the parmacutinase branch of median nerve. Because if he injures this during the release then the patient won't get relief and there will be further parasthesia and more kind of pain or surgery. So if you see this is the median nerve which shows a nice honeycomb appearance if you see along the radial aspect of the nerve you will see a tiny dot which is the parmacutinase branch of the median nerve arising from the radial aspect of the nerve distilling the forearm and then this nerve becomes superficial it pierces the flexor retinaculum at this level or sometimes it goes proximally over it and then becomes superficial to the tunnel there. So that's the parmacutinase branch which you can see the tiny dot it's traversing through the flexor retinaculum and becoming superficial this is the one which the surgeon has to take care of.